Alice and Bob's sifted bit string for the \(X\)  basis will differ due to errors, which are corrected in the reconciliation stage, to produce the identical bit strings called the raw key. Error correction can be performed using a number of schemes [1]}, all of which requires public communication between that leaks \(\lambda _{EC}\)  bits. Alice and Bob then perform a verification step to ensure their raw keys are identical with probability at least \(1-\epsilon _{c}\) , where \(\epsilon _{c}\)  is a pre-agreed correction parameter [2]}, here chosen to be \(\epsilon _{c}=10^{-15}\) . The final stage is privacy amplification [3]}, [1]}, [5]} that reduces the key to length \(\ell \)  bits.
